1,4-hydrogenation of sorbol with Ru complexes

Abstract

The present invention relates to the use of Ru complexes, having a pentamethyl-cyclopentadienyl and a cyclooctadine as ligands, together with some acidic additives for improving the selectivity in the 1,4-hydrogenation of sorbol into the corresponding Z-alkene as major product.

1. A process for the catalytic reduction by 1,4-hydrogenation, using molecular H 2 , of sorbol of formula 
       
         
           
           
               
               
           
         
       
       into the corresponding Z-alkene, of formula 
       
         
           
           
               
               
           
         
         wherein the isomer of configuration Z is predominant; 
       
       wherein the process is carried out in the presence of
 at least one ruthenium catalyst or pre-catalyst of formula
   [Ru(C 5 Me 5 )(COD)(L′) n ]X  (III) 
 
 
       wherein C 5 Me 5  represents pentamethyl-cyclopentadienyl, COD a cyclooctadiene ligand and X represents a non coordinated anion, n represents 2, 1 or 0 and L′ represents a solvent; and
 at least one acidic additive selected from the group consisting of:
 a compound of formula R 3   (3-x) MO(OH) x , wherein R 3  is a R 4  or R 4 O group wherein R 4  is a C 1 -C 10  group, M is P or As and x is 1 or 2; 
 a boron derivative of formula R 3 B(OH) 2 , wherein R 3  is as defined above; and 
 phenol or a phenol substituted by up to three C 1 -C 4  alkyl, alkoxy or carboxylic groups, nitro groups or halogen atoms; 
 
 C 1 -C 12  mono-carboxylic non-amino acid;
 a HOOCCH═CHCOOH di-acid, and the tetronic acid. 
 
 
     
     
       2. A process according to  claim 1 , wherein COD is cycloocta-1,5-diene, cycloocta-1,4-diene, cycloocta-1,3-diene. 
     
     
       3. A process according to  claim 1 , wherein X is ClO 4   − , R 1 SO 3   − , wherein R 1  is a chlorine or fluorine atom or a C 1 -C 8  fluoroalkyl or fluoroaryl group, BF 4   − , PF 6   − , SbCl 6   − , SbF 6   − , or BR 2   4   − , wherein R 2  is a phenyl group optionally substituted by one to five groups of halide atoms, methyl groups or CF 3  groups. 
     
     
       4. A process according to  claim 1 , wherein the at least one acidic additive is a mono-carboxylic acid is selected from the group consisting of:
 a carboxylic acid of formula R 5 COOH, wherein R 5  represents a halogenated or per-halogenated C 1 -C 8  hydrocarbon group; 
 a R 6 CH(OR 6 ) group, R 6  being a hydrogen atom or a C 1 -C 6  hydrocarbon group; and 
 a C 1 -C 12  hydrocarbon group, optionally substituted by one or two ether or ester groups, with the optional substituent being one, two or three C 1 -C 4  alkyl, alkoxy or carboxylic groups, or nitro groups or halogen atoms. 
 
     
     
       5. A process according to  claim 1 , wherein the at least one acidic additive is selected from the group consisting of:
 a compound of formula R 3   2 MO(OH) or R 3 MO(OH) 2 , wherein R 3  is a C 1 -C 6  alkyl or alkoxyl group or a C 1 -C 8  phenyl or phenoxyl and M is P or As; and 
 maleic or glycolic acid and an halogenated or per-halogenated C 1 -C 7  mono-carboxylic acid. 
 
     
     
       6. A process according to  claim 1 , wherein the at least one acidic additive is (BuO) 2 PO(OH), ( t BuO) 2 PO(OH), (PhO) 2 PO(OH), (PhCH 2 O) 2 PO(OH),  t BuPO(OH) 2 , Ph 2 PO(OH), PhPO(OH) 2 , PhAsO(OH) 2 , (Me) 2 AsO(OH), CF 3 COOH, HCF 2 COOH, maleic or fumaric acid, glycolic acid, pyruvic acid, sorbic, acetic or oleic acid, tetronic acid, C 6 H 13 B(OH) 2 , PhB(OH) 2 , p-OMe-benzoic, benzoic or p-(COOMe)-benzoic acid, phenol, 3,5-dimethoxy-phenol or 2-methoxy-phenol. 
     
     
       7. A process according to  claim 1 , wherein said process is carried out in the presence of a solvent selected amongst the C 1 -C 12  alkyl ketones, esters, ethers or chlorinated alkanes and mixture thereof. 
     
     
       8. A process according to  claim 1 , wherein the at least one acidic additive is in a total amount of about 0.1 to 100 molar equivalents, relative to the compound (III).